Molten metal, particularly molten aluminum, in practice generally contains entrained solids which are deleterious to the final cast metal product. These entrained solids appear as inclusions in the final cast product after the molten metal is solidified and cause the final product to be less ductile or to have poor bright finishing and anodizing characteristics. The inclusions may originate from several sources. For example, the inclusions may originate from surface oxide films which beome broken up and are entrained in the molten metal. In addition, the inclusions may originate as insoluble impurities, such as carbides, borides and others or eroded furnace and trough refractories.
Porous ceramic foam materials are known to be particularly useful in filtering molten metal, as described in U.S. Pat. No. 3,893,917 for "Molten Metal Filter" by Michael J. Pryor and Thomas J. Gray, patented July 8, 1975, and also as described in U.S. Pat. No. 3,947,363 for "Ceramic Foam Filter" by Michael J. Pryor and Thomas J. Gray, patented on March 30, 1975, U.S. Pat. No. 4,081,371 for "Filtering of Molten Metal" by John C. Yarwood, James E. Dore and Robert K. Preuss, patented March 28, 1978, and U.S. Pat. No. 4,024,056 for "Filtering of Molten Metal" by John C. Yarwood, James E. Dore and Robert K. Preuss, patented May 17, 1977.
These ceramic foam materials are particularly useful for filtering molten metal for a variety of reasons included among which are their excellent filtration efficiency, low cost, ease of use and ability to use same on a disposable, throwaway basis. The fact that these ceramic foam filters are convenient and inexpensive to prepare and may be used on a throwaway basis requires the development of means for easily and conveniently assembling and removing porous, molten metal filters from a filtration unit while providing a highly efficient filtration assembly.
Since the filters are designed to be a throwaway item, it is essential to provide an effective means of seating the filters in place in its holder which is easy to assemble and disassemble. The holder or filter chamber itself is normally an itegral part of a trough, pouring pan or tundish, and should be constructed of refractory materials resistant to the molten metal similar to those used in standard trough construction. The filter plate is normally sealed in place using a resilient sealing means or gasket type seal peripherally circumscribing the filter plate. In order to effectively place the filter plate in position in the filter chamber, the prior art teaches the provision of a bevelled peripheral surface on the filter plate onto which the gasket seal is placed. The filter plate is then sealed in place by exerting a vertical pressure downwards on the filter plate in the filter chamber which is provided with a corresponding bevelled surface. It has been found that, as a result of the force exerted on the filter plate during assembly in the filter chamber, structural damage may result to the filter plate which could result in metal leakage and/or ineffective metal filtration. Naturally also, removal of the filter plate has been found to cause difficulties.
Furthermore, filtration assemblies commonly in use normally provide that the filter plate is horizontally disposed in the filter chamber. This horizontal disposition results in occupying a considerable amount of space in the metal line. It is desirable to provide a filtration assembly wherein the filter plate is vertically disposed since the vertical disposition will result in a space-saving arrangement.
Vertical dispositions of filter plates are known from, for example, U.S. Pat. No. 4,092,153. However, this patent simply teaches providing the filter plate with a bevelled peripheral surface mating with a like bevelled surface in a filter chamber so that the filter plate is inserted in the chamber in a similar manner as with the horizontally disposed filter plates. While the '153 patent effectively teaches a vertically disposed filter plate, it has been found in practice that this vertical disposition arrangement is not entirely satisfactory in view of metal freeze-up problems and problems associated with removal of the spent filter.
Accordingly, it is a principal object of the present invention to provide an improved molten metal filtration apparatus which is easy to use on a commercial scale.
It is a further object of the present invention to provide an improved molten metal filtration apparatus which is characterized by the vertical disposition of the filtration assembly.
It is a still further object of the present invention to provide an improved filtration apparatus as aforesaid which is characterized by convenient placement and removal of the filtration assembly.
Further objects of the present invention will appear hereinbelow.